Who is Lord Shiva's replacement from Sauptika Parva?

Question

The 17th chapter of Sauptika Parva from the Mahabharata says that Brahma creates someone to replace Shiva for create beings.

Having waited in expectation of Rudra for a very long time, the Grandsire, by a fiat of his will, invoked into existence another being for making him the creator of all kinds of living things. Beholding Girisha plunged into the waters, this (second) being said unto his sire, "If there be no being born before me, then I will create living creatures!" His sire replied unto him, saying, "There is no other first-born being besides thee! This Sthanu has plunged into the water! Go and create living creatures, without any anxiety!"

That being then created many living creatures, having Daksha for their first, who created all these creatures of four kinds. As soon, however, as they were created, they ran O king, towards their sire, afflicted with hunger and desirous of devouring him. The second being whom Brahma had created, thereupon ran towards him, desirous of protection from his own offspring. And he said unto the Grandsire, "O illustrious one, protect me from these, and let these creatures have their food assigned unto them!" Then the Grandsire assigned herbs and plants and other vegetables as their food, and unto those that were strong he assigned the weaker creatures as the means of sustenance. Their sustenance having been thus assigned, the newly-created creatures all went away to regions they desired, and cheerfully multiplied by union with their respective species.

After the creatures had multiplied and the Grandsire had become well pleased, the first-born rose from the water and beheld the living creation. He saw that diverse kinds of creatures had been created and that they had multiplied by their own energy. At this sight, Rudra became angry and caused his procreative limb to disappear in the bowels of the Earth.

But, who is he? Does any other scriptures mention about him?

Answer 1

Here is a similar account from Veda, let's go over this first and then we can see the contrast with Mahabharatam.

In an event in Śatapatha Brāhmaṇa of Śukla Yajurveda, Prajapathi (in your case Brahma) performed austerity for a Sāṃvatsara (in your case He waited patiently for certain time for someone to do creation) , meaning one Solar cycle year, and upon its dawn (Uṣas/Auṣasī) arose a child (so this child is not Rudra of the Mahabharata which Brahma was waiting), meaning the union of Sāṃvatsara and Uṣas gave birth to a child. So, who is this child? And what is the name of this child?

Upon birth, this child cried (arodīt); Prajāpati held this child and said “my son you are Rudra” (So Brahma called this Child Rudra and not the actual Rudra) as he is the first roar/sound. This is why Rudra is the primordial roar. Hence, please note that Rudra didn’t come as the boy, this boy was called Rudra. So this boy was not satified and asked for another name (in your case the boy asked a different question) This boy could not be contained and wished to encompass everything and so said, “with my name I have to become greater” and asked for another name/title. Prajāpati said “you are Śarva” and so the water became him, the boy grew in greatness and kept asking for more names. He was named Paśūpati, from him emerged flora/fauna. He was named Ugra (the fierce one), Vayu/Wind/Air became him. He was named Aśani, lightning became him and so did thunder. He was named Bhava, the rain became him and the Divinity of rain is Parjanya. He was named Mahādeva, the highest Divinity, and the moon (Soma) became him; hence He, Mahādeva with a moon on his head. He was named īśhana (the authority/the ruler), the Sun became him (hence the title Mīḍhuṣṭama/मीढुष्टम meaning Sun in Taittirīya Saṃhitā 4.5.5).

In Kausitaki Brāhmaṇa of Rig Veda, the event is very similar but with slight changes.Then if we read Vājasaneyi Saṃhitā of Yajur Veda it has another account for creation involving Rudra and Prajapati, and the list goes on....

Conclusion: if you read different literature across time, there is going to be some alterations. But the intent and core content is the same. So if you read the various stories associated with Rudra and Brahma, the way Rudra emerges is diverse and vast. Why?

Because the Vedic event revolve around Yajñá that explains the raw, unmanifested nature of Rudra who can exist in all, the innate self of all. depending on the cause and the event, the concept of Rudra manifests, so Rudra’s expansion is countless. Rudra is a contradiction that doesn’t confine to any class or category. One cannot address Rudra without finding a polar opposite to it, that is why Rudra is called “that which is not”. So one has to be very attentive to the type of Rudra while resiting Rudriya (Hymns of Rudra). Because of this diversity and encompassing name of Rudra He is called Viṣvarūpam or Pururūpam or Virūpam (the universal or cosmic form with multiple flavors and multifold) or Viśvaiśvaryam RV 2.33/TS4.5.4/TA10.23.1/SU1.11. Śrī Rudram and Śatarudriya present the totality of Rudra’s omnipresence (which we will explore here) – especially Taittirīya Saṃhitā 1.8.6, which says “एक एव रुद्र न द्वितीयाय तस्थुर्” meaning “There is a Rudra without a second”. Hence, Rudra cannot be confined to a group or a singular entity. Rudra is the UNMANIFEST RAW concept from which anything and everything manifests, yet that manifestation is neither separate nor an independent entity. Hence, Rig Veda calls him सव-धाव्ने = self-reliant and सवराजः = self-governing RV5.58/7.46. This, in turn, gave a foundation to the Svetasvatara Upaniṣhad (one among the 18 primary Upaniṣhads) and also the later Atharvashiras Upaniṣhad (minor Upaniṣhad).

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